Purpose: To investigate the clinical characteristics and treatment outcomes of immunoglobulin G4-related ophthalmic disease (IgG4-ROD) in Korean patients. Design: A multicenter, retrospective case series study. Participants: A total of 341 patients with IgG4-ROD from 24 hospitals in Korea. Methods: The medical records of all patients with IgG4-ROD were reviewed, which were consistent with comprehensive diagnostic criteria. The demographic, clinical, histopathological, and laboratory data were also collected. Main Outcome Measures: Frequencies of extra-lacrimal gland and extraorbital involvement and treatment outcomes with potential predisposing factors. Results: Among the 341 patients with IgG4-ROD who were enrolled, 155 (45.5%) had definite IgG4-ROD. Among the 155 patients with definite IgG4-ROD, extra-lacrimal gland involvement was observed in 53 patients (34.2%) and was associated with older age, male sex, unilaterality, and higher serum IgG4 levels. Extraorbital involvement was observed in 52 of 77 patients (67.5%) with definite IgG4-ROD who underwent adequate systemic evaluation. Regarding treatment outcomes, 130 patients with definite IgG4-ROD who were followed up for > 6 months were included for the analysis; 93 patients (71.5%) achieved remission, and 40 patients (30.8%) attained steroid-free remission (SFR). Surgical debulking was significantly associated with remission and SFR, whereas initial use of an immunomodulator with a steroid showed no significant association with the treatment outcome. The highest serum IgG4 tertile was negatively associated with SFR. Relapses occurred in 24 (28.9%) of 83 patients who experienced remission, and underlying diabetes was an associated risk factor. Conclusions: Extraorbital involvement was detected in more than half of the patients with definite IgG4-ROD, emphasizing that broad systemic evaluation is warranted for these patients. Disease remission was achieved in 71.5% of patients, but relapse occurred in a significant number of patients. Steroid-free remission was positively associated with surgical debulking. These findings suggest that the surgical debulking of the lesions and patient tolerability to steroid therapy may affect treatment outcomes in IgG4-ROD. Financial Disclosure(s): Proprietary or commercial disclosure may be found after the references. Ophthalmology 2025;132:995-1004 (c) 2025 by the American Academy of Ophthalmology. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).